Multiplex communications – Wide area network – Packet switching
Patent
1984-06-29
1986-03-04
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
375107, 34082552, H04J 306, H04L 700
Patent
active
045743762
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to an apparatus in a telecommunication system for activating subscriber terminals in a digital subscriber connection e.g. including a line terminal, a network terminal and one or more subscriber terminals.
BACKGROUND ART
It is known to switch subscribers from idling state to activated state with the aid of special activation signals in the form of DC signals.
DISCLOSURE OF INVENTION
A problem occuring in DC activation is the requirement of detecting different DC current levels in order to distinguish between idle condition currents and activation currents. Since the idle condition currents are used to maintain certain functions in the terminal during the idling state also, the idle condition current level is also limited by the level of the activation signal, there being limits to how low the former may fall and how high the latter may rise. This rerults in a small margin between the different voltage levels and thus increases the sensitivity to noice.
The apparatus in accordance with the invention is characterized by the claim, and solves the problem by the activation being carried out with the aid of binary codes in the form of continuously-sent bit patterns. Detection of the codes is carried out digitally.
The apparatus in accordance with the invention is mainly applied in activating a digital transmission link in which one terminal contains a stable clock pulse oscillator functioning as a master clock, and the other terminal contains a slave clock which is plesiochronous in relation to the master clock.
In the described apparatus, acitivation is performed between a network terminal NT assigned to the subscriber installation and a line terminal LT assigned to the station equipment. The line terminal LT contains a stable master clock and the network terminal LT contains a slave clock working plesiochronously in relation to the master clock. Activation can be initiated either from the subscriber side of a connection or from the station side.
In activation from the subscriber side an activation request from a subscriber starts a transmitter in the network terminal NT. A code (continuous bit pattern) is sent with plesiochronous bit rate from the subscriber side (terminal NT) to the station side (terminal LT). The code is detected in the line terminal LT of the station side and is interpreted as an activation request. The station accepts the activation request by triggering an activation order. The activation order starts a transmitter in the line terminal LT and connects it for transmission of data in frame format back again to the network terminal NT under control of the master clock. The local slave clock on the subscriber side is synchronized to the rate of the master oscillator taken from the bit flow received from the line terminal LT. When the frame format is detected, the network terminal transmitter is switched over for sending out data in frame format back again to the station side. On the station side, the frame format-frame synchronization is detected and there is thus indicated that the link between subscriber side and station side is bit- and frame-synchronous, the activation thereby being completed.
When activation is initiated from the station side, no activation request is sent and an activation order is released directly. This is because an activation order is always triggered from the station/master side. The activation order starts the line terminal transmitter, which then sends a code in the form of a continuous bit flow to the network terminal NT. The local clock on the subscriber side is synchronized to the rate in the received bit flow, the code is detected and the transmitter on the subscriber side (the terminal NT) is started. A code is sent from the subscriber to the station. The code is detected on the station side and the line terminal transmitter is switched over to transmission of the data in frame format back again to the subscriber network terminal. The frame format-frame synchronism is detected in the network terminal and its tran
REFERENCES:
patent: 3823387 (1974-07-01), McClellan
patent: 4143246 (1979-03-01), Smith
patent: 4314109 (1982-02-01), Sekiguchi et al.
patent: 4355386 (1982-10-01), Binz et al.
Olms Douglas W.
Scutch III Frank M.
Telefonaktiebolaget L M Ericsson
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